In the assembly of various types of electronic apparatus, such as communication transmission equipment, a plurality of printed circuit boards are plugged into connector plugs of a backplane assembly for interconnection of the boards to other electronic apparatus. In order to facilitate the insertion of plug-in portions of the boards into the connector plugs, support shelves are provided for supporting the boards and for aligning the boards with the connector plugs. Typically, a plurality of support shelves are horizontally mounted on a vertical bay frame in a spaced relationship from each other and include guide tracks or channels formed on upper and lower surfaces of the shelves. The upper guide tracks of one shelf cooperate with the lower guide tracks of an adjacent shelf to slidably receive lower and upper edges of the printed circuit boards, respectively. In this manner, the support shelves provide support for the printed circuit boards, proper alignment of the boards relative to the connector plugs of the backplane assembly, and orderly connection of the boards to the connector plugs.
As the electronics of transmission equipment becomes more and more complex, epoxy-coated metal printed circuit boards in relatively closely-spaced relationship (e.g., 1/2 inch centers) are being used to replace previously used epoxy-coated fiber boards. Accordingly, it is particularly important that the edges of the guide tracks and all other board-engaging surfaces of the shelves are smooth and free from burrs and sharp corners to avoid damage to the metal board coating. Otherwise, scratching or marring of the epoxy insulating surfaces of the metal boards could occur as the boards are being inserted into the backplane assembly, which could cause shorting or other malfunction of the boards during the operation of the transmission equipment. Further, scratching through the epoxy insulating coating of the printed circuit board to the underlying metal surface also can cause oxidation of the metal board where the scratch occurs, with subsequent deterioration of the board and flaking of the epoxy coating.
Additionally, the closely-spaced relationship of the metal printed circuit boards produces a weight concentration of equipment in a relatively small space. Consequently, the shelf must possess high strength characteristics and be highly resistive to flexing and bending when the plurality of printed circuit boards are supported thereon.
During the operation of the transmission bay module, the closely-spaced printed circuit boards supported on the shelves also generate a great deal of heat which must be dissipated from the shelves to insure continued uninterrupted operation of the printed circuit boards. Accordingly, it is desirable to provide support shelves which promote air circulation between the printed circuit boards and facilitate heat dissipation from the transmission bay module.
Further, occasionally a warped printed circuit board must be inserted into one of the connector plugs of the backplane assembly. It then is difficult, if not impossible, to align the plug-in portion of the board with the connector plug for proper insertion of the board into the plug unless the support shelves have facilities for accurately aligning both the upper and lower edges of the board with the connector plug.
In the past, the support shelves for the printed circuit boards have been fabricated in various manners, including die casting, plastic molding and metal fabricating. For example, the U.S. Pat. No. 3,731,157 to W. A. Reimer discloses a support shelf stamped as a unitary structure from a single sheet of stock material. The shelf includes a plurality of spaced upper channels for receiving lower edges of printed circuit boards, and a plurality of spaced lower alignment notches formed in vertical alignment with respective ones of the upper channels, for receiving upper edges of printed circuit boards. The shelves are arranged in a vertically spaced relationship such that the upper channels of one shelf cooperate with the lower alignment notches of an adjacent shelf thereabove to receive and align printed circuit boards therebetween.